The Role of ERRFI1+808T/G Polymorphism in Diabetic Nephropathy.

Nephropathy is a common diabetes complication. ERRFI1 gene which participates in various cellular pathways has been proposed as a candidate gene in diabetic nephropathy. This study aimed to investigate the role of +808T/G polymorphism (rs377349) in ERRFI1 gene in diabetic nephropathy. In this case-control study, patients including diabetes with nephropathy (DN=104), type 2 diabetes without nephropathy (DM=100), and healthy controls (HC=106) were included. DNA was extracted from blood, and genotyping of the +808T/G polymorphism was carried out using PCR-RFLP technique. The differences for genotype and allele frequencies for +808T/G polymorphism in ERRFI1 gene between DN vs. HC and DN+DM vs. HC were significant (P<0.05) while no significant difference between DN and DM was observed. The allele frequencies were significantly different in DN vs. HC and DN+DM vs. HC in males but not in females. G allele of +808T/G polymorphism in ERRFI1 gene has no significant role in development and progression of diabetic nephropathy in diabetes patients while it is a risk allele for developing diabetes in Iranian population.

Diabetes is the leading cause of chronic kidney disease and end stage renal disease (ESRD) (4).
The death rate of kidney disease is 17 times higher in individuals with diabetes than non-diabetics (5).  (16)(17)(18). The expression of ERRFI1 gene is rapidly increased due to stress, mechanical strain and the presence of various hormones and growth factors, which finally leads to hypertrophy (15-17, 19, 20). This gene has a responsive element to insulin, and its expression is elevated in diabetes (21,22). The ERRFI1 gene has high expression in the liver and kidney, and has a moderate to low expression in brain, lung, placenta, heart, and thymus tissues (23). Increasing the expression of ERRFI1 in beta cells results in apoptosis and cell death (24). ERRFI1 seems to reduce the mass of beta cells through its antagonistic role in the EGFR signaling pathway (24,25). ERRFI1 gene transcription is enhanced by stress-activated protein kinases (SAPKs) which can lead to hypertrophy and progression towards nephropathy (15). There is a mutual relationship between SAPKs and ERRFI1 gene. In nephropathy, SAPKs activate ERRFI1 transcription and activated ERRFI1 triggers the stability and expression of SAPKs (15). The +808 (T/G) (rs397349) variant is located in the third intron of the downstream transcription site of ERRFI1 gene (20). The association of ERRFI1 gene polymorphism with fasting plasma glucose and its protective effect in DN has been reported (20). The purpose of the present study was to investigate the association between +808 (T/G) polymorphism and DN in a group of Iranian diabetic patients.

Statistical analysis
The unpaired t-test was used to compare mean ± SD of clinical and biochemical data between studied groups. Fisher's exact test was used for calculating hardy Weinberg equilibrium for small numbers (26). Odds ratios (OR) and 95% confidence intervals (CI) were calculated using chisquare test. P-value <0.05 was considered statistically significant. All statistical analyses were performed by SPSS software version 16.

Clinical and biochemical characteristics
Clinical and biochemical characteristics of studied groups are represented in Table 1

Genotypes and alleles distribution
The distribution of genotypes and alleles is shown in ( We found a gender specific association in different groups (Table 3)    DM groups (P = 0.44).
Then DN and DM groups were pooled together, and clinical and biochemical parameters between individuals with GG+GT genotypes (allele G) and TT genotype (allele T) were compared ( Table 4).
The age, duration of diabetes, BMI, FBS, urea and uric acid were higher, and SBP, DBP, A1c and ACR were lower in GG+GT group in comparison with TT group, although it was not statistically significant (P> 0.05). There was no significant difference in any biochemical parameters between the two groups with GG+GT and TT genotypes.

Discussion
The results of the current study showed a significant association between +808T/G variant populations. This is the first time that the association of this polymorphism with nephropathy has been studied in the Iranian population.
In conclusion, there was no significant association between ERRFI1 +808T/G polymorphism and diabetic nephropathy in Iranian population while T allele of this polymorphism has protective role against diabetes in the studied population. It seems that ERRFI1 polymorphism has diverse function in various populations which might be due to various clinical manifestations or pathogenesis in different ethnic groups.
It will be interesting to investigate the relationship between this polymorphism with diabetes nephropathy in other populations.